The basic hashtable is intended to be used to support a variety
of different datastructures such as map, set, multimap,
multiset, linkedmap, generationcache, etc.
Consequently its interface is fairly primitive.
The basic hashtable supports copy-on-write style functionality
using SharedBuffer.
The change introduces a simple generic function in TypeHelpers for
specifying hash functions. The idea is to add template
specializations of hash_type<T> next to the relevant data structures
such as String8, String16, sp<T>, etc.
Change-Id: I2c479229e9d4527b4fbfe3b8b04776a2fd32c973
